Removing unstable sulfur compounds from crude oil

ABSTRACT

A crude oil which contains at least 0.1 wt % unstable sulfur compounds is treated in a reaction zone at low temperature to convert at least 50 wt % of the unstable sulfur compounds contained therein. The reaction and removal of sulfur from the crude may be facilitated by contacting the crude oil with a catalytic material in the presence of a stripping fluid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of and claims priority to U.S. patentapplication Ser. No. 12/332,130, titled “Removing Unstable SulfurCompounds From Crude Oil,” and filed on Dec. 10, 2008. The entirecontents of the foregoing application is hereby incorporated herein byreference.

TECHNICAL FIELD

The present invention is directed to a method for purifying a crude oilin preparation for shipping, transporting or refining.

BACKGROUND

Sulfur-containing crude oils continue to be a challenge for the shipperand refiner. Sulfur compounds in crude may present hazards to thoseengaged in handling, transporting or shipping the crude. They mayintroduce corrosion issues for transportation vessels, storage vessels,reaction vessels, separation vessels, piping and pumps used in thetransportation and handling of sulfur containing crudes. They mayintroduce unique challenges for distilling such sulfur-containing crudeoils.

U.S. Pat. No. 6,841,062 describes a crude oil desulfurization processwhich comprises hydrodesulfurizing a crude oil feed in a crudedesulfurization unit. As described, when the product sulfur ismaintained at less than 1 wt % based on feed, and preferably less than0.75 wt % based on feed, reaction conditions in the crudedesulfurization unit include a reaction temperature between about 315°C. and 440° C. (600° F.-825° F.), pressures from 6.9 MPa to about 20.7MPa (1000-3000 psi), and a feed rate (vol oil/vol cat hr) from 0.1 toabout 20 hr⁻¹. Hydrogen circulation rate is general in the range fromabout 303 std liter H₂/kg oil to 758 std liters H₂/kg oil (2000-5000standard cubic feet per barrel).

Some crude oils contain significant amount of unstable sulfur compounds.Under mild heating, these sulfur components react by hydrolysis and/orthermal degradation to form volatile sulfur compounds, including H₂S.These reactions usually result in a slow but continuous hydrogen sulfidegeneration during the transportation of those crudes, which is one ofthe major risks or hazards on transporting such crude oils. Thesereactions also cause difficulties in refining those crude oils. At hightemperature, as in the atmospheric and the vacuum distillation towers,the H₂S production rate in the overhead of a distillation tower may behigh enough to cause upsets in the tower. Currently, there is noexisting technology to remove or convert unstable sulfur compounds inthe crude oils, and crude containing high unstable sulfur has to beblended with other crudes in refineries. Overall, the need for blendingseverely limits the refiner's capacity in processing these unstablesulfur containing crudes. As a result, such crudes are usually sold at adiscount in the market. Thus, solving the H₂S evolution problem couldsubstantially improve both the marketability and the value of crudessuch as Eocene.

SUMMARY

In embodiments, the present process is provided for removing sulfurcompounds from crude oils, wherein the sulfur compounds are unstable atnormal handling and processing conditions. Thus, the present inventionprovides a process for reducing the sulfur content of a crude oil,comprising heating a crude oil containing at least 0.1 wt % unstablesulfur compounds at conditions sufficient to remove at least 50% of theunstable sulfur compounds contained therein.

Thus, a desulfurized crude oil is prepared by heating a crude oilcontaining at least 0.1 wt % unstable sulfur compounds at a temperaturein the range of 100° F. to 400° F. to convert at least 50% by weight ofthe unstable sulfur from the crude oil. In embodiments, the crude oil isheated at a temperature in the range of 100° F. to 450° F. and at apressure in the range of 15 psia to 200 psia for a time period in therange of 1 minute to 60 minutes.

In some such embodiments, the heated crude oil is contacted with acatalytic material selected from the group consisting of inorganic ororganic acids, particulate molecular sieves, dissolved metal ions,metal-containing slurry in an organic or aqueous fluid and a particulatecatalyst comprising a metal component on an inorganic oxide matrix.

In another embodiment, the process for reducing the sulfur content of acrude oil comprises heating a crude oil containing at least 0.1 wt %unstable sulfur compounds at a temperature in the range of 350° F. to600° F. to convert at least 50% of the unstable sulfur compoundscontained therein.

In some such embodiments, the crude oil is heated in the absence ofadded catalytic material

In some such embodiments, the process further comprises contacting theheated crude oil with a stripping fluid to facilitate the removal ofvolatile sulfur compounds contained in the heated crude oil.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 and FIG. 2 illustrate two embodiments of the invention, showingthe heating zone and the reaction zone for removing the unstable sulfurcompounds from crude oil.

DETAILED DESCRIPTION

As used herein, unstable sulfur compounds are those compounds in crudeoil which react, in the absence of added hydrogen and without an addedcatalytic material, when the crude oil is heated to elevatedtemperatures to form normally gaseous products. Hydrogen sulfide is oneof the products generated from the reaction of the unstable sulfurcompounds. However, sulfur-containing hydrocarbonaceous molecules mayalso be present in the gas phase effluent from the heated crude oil,either resulting from the reaction of unstable sulfur compounds, or byvaporization of volatile sulfur containing hydrocarbons. In embodiments,unstable sulfur compounds include sulfur compounds having the genericformula S_(x), wherein x is >1 and S represents a sulfur atom. Inembodiments, x is a value in the range from 1 to 10.

In embodiments, unstable sulfur compounds include polysulfides, whichare a class of polymeric materials with the general formula for therepeat unit: —[(CH₂)_(m)+S_(x)]_(n)—, where m is the number of CH₂repeating units, x is the number of sulfur atoms and n indicates thenumber of repeat units. In some such embodiments, x is a value in therange from 1 to 10, m is a value in the range of 1 to 10, and n is avalue in the range of 1 to 20.

In their simplest form, inorganic polysulfides are ionic compounds withanions having the general formula S_(n) ²⁻. In some such embodiments, nis a value in the range of 1 to 10.

In embodiments, unstable sulfur compounds include polysulfanes, whichare un-branched chains of sulfur atoms terminating with hydrogen andhaving the general formula H₂S_(x), where x>1. In some such embodiments,x is a value in the range of 1 to 10.

The reaction of the unstable sulfur compounds involves conversion tovolatile sulfur compounds at temperatures as low as 100° F. Inembodiments, the volatile sulfur compounds include H₂S, low molecularweight mercaptans (C_(x)H_(2x)S, where x≧1), carbon disulfide (CS₂),carbonyl sulfide (OCS) and mixtures thereof.

The hydrocarbon streams which may be treated as disclosed herein may becrude oils, synthetic crude oils; atmospheric gas oils; fuel oils;diesel oils and the like and combinations thereof in variousnon-limiting mixtures. In embodiments, The hydrocarbon streams maycontain other components including, but not necessarily limited to,water, CO₂, asphaltenes, acids, naphtha, paraffins, olefins, oxygenatedhydrocarbons, oxygen, nitrogen, sulfur, sulfur derivatives, disulfidesand aromatics, and the like and combinations thereof.

The process for removing unstable sulfur compounds from the crude takesplace in a treatment zone comprising a heating step, a reaction step anda separation step. The steps may be performed simultaneously in a singlevessel, sequentially in a single vessel or sequentially in separatevessels. Likewise, any two of the steps may be performed simultaneouslyin a single vessel, sequentially in a single vessel or sequentially inseparate vessels, with the remaining step being performed in a separatevessel. In embodiments, the heating is said to take place in a heatingzone, reactions are said to take place in a reaction zone andseparations are said to occur in a separation zone. In all cases, theheating zone may involve the same volume or different volumes from thereaction zone and the reaction zone may involve the same volume ordifferent volumes from the separation zone.

In the present invention, a crude oil containing at least 0.1 wt %unstable sulfur compounds is heated at conditions sufficient to convertat least a portion of the unstable sulfur compounds contained therein.In embodiments, the crude oil is heated at conditions sufficient toremove at least 50% of the unstable sulfur compounds contained therein.In some such embodiments, reaction conditions are sufficient to convertat least 75 wt %, or even 90 wt %, of the unstable sulfur compounds inthe crude to volatile sulfur compounds.

Process conditions within the treatment zone are selected to achieve thedesired removal of the unstable sulfur compounds. Thus, the crude oil isheated at a temperature within the range of 100° F. to 800° F. and at apressure of 15 psia and above for a time period of up to 120 minutes forremoving the unstable sulfur compounds. In embodiments, the crude oil isheated at a temperature in the range of 100° F. to 600° F. and at apressure of 15 psia and above.

Relatively lower temperatures may be used when catalytic materials areemployed to facilitate the reaction of unstable sulfur compounds. Insome such embodiments, the crude oil is heated at a temperature in therange of 100° F. to 450° F. and at a pressure in the range of 15 psia to200 psia for a time period in the range of 1 minute to 60 minutes. Otherexemplary temperature ranges include a range of 100° F. to 350° F. Otherexemplary residence time ranges include the range of 5 minutes to 50minutes or the range of 10 minutes to 40 minutes. Other exemplarypressure ranges include the range of 15 psia to 150 psia. Reaction ofthe unstable sulfur compounds in the presence of a catalytic material inthe temperature range of 450° F. to 800° F. will result in a rapidreaction rate. Such rapid reaction rates are generally not detrimentalto the process for removing the unstable sulfur compounds; the hightemperature reaction may be selected if the desulfurized crude oil ispassed directly from the treatment zone to a distillation column.

While the temperature of the crude oil may vary to some extent as itpasses through the treatment zone, the temperature during each step willbe maintained within the specified range.

The unstable sulfur compounds may be removed in a thermal(non-catalytic) process. The unstable sulfur compounds may besatisfactorily converted at a temperature in the range of 100° F. to450° F., though the reaction rate will be lower and the reaction timelonger than in the catalytic case. Thus, in embodiments, at least 50% ofthe unstable sulfur compounds are converted when the crude oil is heatedat a temperature in the range of 350° F. to 600° F. For example, thecrude oil is heated at a temperature in the range of 350° F. to 600° F.and at a pressure in the range of 15 psia to 200 psia for a time periodin the range of 1 minute to 60 minutes. Other exemplary temperatureranges include the range of 350° F. to 500° F. Other exemplary residencetime ranges include the range of 5 minutes to 50 minutes or the range of10 minutes to 40 minutes. Other exemplary pressure ranges include therange of 15 psia to 150 psia.

The crude oil may be treated to remove the unstable sulfur molecules atany time during the production, transportation, handling or otherwiseprocessing of the crude oil. In embodiments, the treatment zone may besituated at the wellhead or its associated production facility fromwhere the crude oil is produced from the petroleum resource. Crude oilthus treated is more safely sent to tankage, loaded into a vessel foroverland and/or sea transport or sent by pipeline.

In embodiments, the treatment zone is situated at a loading facility,for loading the crude oil into a vessel for transport, via ship, barge,train, truck or the like. In some such embodiments, it is desirable tominimally heat the crude oil, while optionally using a catalyst, and toselect an appropriate stripping fluid rate and residence time to effecta desired removal of unstable sulfur compounds from the crude oil at arelatively low temperature. One effect of minimally heating the crudeoil is the low cooling required before the treated crude oil is loadedfor transport. In some such embodiments, the crude oil is heated to atemperature in the range of 100° F. to 300° F. during the sulfurtreatment.

In embodiments, the treatment zone may be integrated into a refinery. Insome such embodiments, the crude passes from the sulfur removaltreatment zone directly and without substantial cooling into a crudeunit for distillation separation of the crude oil into its componentstreams. For this application, the crude oil may be heated totemperatures up 800° F. within the treatment zone. Stripping fluidselection and rate, and the optional use of a catalytic material isselected to accommodate the elevated temperature. This integratedprocess has a feature of reduced equipment and energy requirements overa stand-alone treatment zone. In some embodiments, the crude oil isreacted in the treatment zone at a temperature in the range of 100° F.to 600° F. for a time sufficient to remove at least a portion of theunstable sulfur compounds. The converted crude oil is then furtherheated to distillation temperature in a following heating zone, and fromthere passed to the atmospheric crude column. The crude oil which istreated to remove unstable sulfur compounds in a process unit which isintegrated with the refinery may be passed through a desalting unit forremoving water and inorganic products from the crude prior to thetreatment zone.

In embodiments, the process for removing the unstable sulfur compoundsfrom crude oil may be conducted in the absence of added hydrogen. Whilehydrogen may be used as at least one of the components of a strippingfluid, and while hydrogen or a hydrogen containing gas may be used toblanket the crude oil during a heating step, a reaction step and/or aseparation step, the use of hydrogen, alone or in combination with oneor more other gases, is not required.

In embodiments, aqueous solutions containing sulfur-containingcompounds, such as ammonium sulfide or sodium thiosulfate, may be addedto the treatment zone for contacting with the crude oil to remove theunstable sulfur compounds contained therein. The resulting solutioncontaining an increased amount of sulfide and elemental sulfur is asfollows:(NH₄)₂S+nS°⇄(NH₄)₂S_(n)where n is a value in the range of 1 to 10. In embodiments, theresulting (NH₄)₂S_(n) product is removed from the treatment zone andtreated to recover the ammonium sulfide reactant.

The heating zone provides heat energy to increase and/or maintain thetemperature of the crude oil. The heating zone may be any devicesuitable for heating a liquid to an elevated temperature, such asboilers, heat exchangers, furnaces and process heaters, electricalheaters, gas fired heaters, oil fired heaters, coal fired heaters andthe like. In another embodiment, the heating zone may be integrated intoother heating operations, such as within a refinery. In embodiments, theheating zone is a pipe or conduit through which the crude oil istransmitted. The pipe or conduit comprises a heating section, andoptionally a reaction section after the heating section. The treatmentzone will be of sufficient dimensions to permit a desired amount ofsulfur removal from the crude.

The crude oil may further be contacted with a stripping fluid within thetreatment zone to facilitate the removal of volatile sulfur speciescontained therein. Any gas phase material that does not detrimentallychange the crude oil during the separation process may be used as astripping fluid. Suitable gas streams to be used in stripping out thevolatile sulfur compounds include, but are not necessarily limited to,natural gas, methane, ethane, propane, butane, pentane and heavierhydrocarbons, nitrogen, carbon dioxide, argon, helium, hydrogen, carbonmonoxide and combinations thereof. In embodiments, the stripping fluidcomprises a gas-phase material selected from the group consisting ofnatural gas, a hydrocarbonaceous gas, nitrogen and mixtures thereof. Inembodiments, the stripping fluid comprises methane or mixtures ofmethane, ethane, and small amounts of propanes, butanes and yet smalleramounts of heavier hydrocarbons, in various non-limiting mixtures. Inembodiments, the stripping fluid is a process gases. Typical processgases are generated during petroleum processing, and comprise gasmixtures containing at least one of methane, ethane, propanes andbutanes in various compositional ratios, with optionally smaller amountsof heavier hydrocarbons.

The gas phase material is provided to the treatment zone at or above thepressure of the crude oil in the treatment zone, and at ambienttemperatures or above. In embodiments, the gas phase material may beintroduced into treatment zone at a temperature which is lower than,higher than or equal to the temperature of the crude oil entering thezone. In some such embodiments, the gas phase material is provided tothe treatment zone at a temperature in the range of 100° F. to 450° F.In other embodiments, the gas phase material is provided to thetreatment zone at a temperature in the range of 350° F. to 600° F., orin the range of 600° F. to 800° F. The gas phase material is provided tothe treatment zone at a linear velocity and a rate to facilitate theremoval of at least 50% of the volatile sulfur compounds from the crudeoil.

In embodiments, the gas phase material may be added to the crude as thecrude enters the treatment zone, it may be added as the crude passesthrough the treatment zone, or it may be added as the crude leaves thetreatment zone. The stripping fluid is provided to the crude oil throughgas distributors known for this purpose. Non-limiting examples include agas injection port, at least one sieve tray or at least one bubble trayover which the crude oil passes.

In embodiments, the process and system described herein for removing theunstable sulfur compounds from the crude oil have an absence of addedcaustic alkali compounds (e.g. alkali metal hydroxides such as NaOH).There is also an absence of added amine compounds, oxidation agents andorganic reducing agents, such as hydrazine, oximes, hydroxylamines,carbohydrazide and erythorbic acid.

The treatment zone may further contain one or more catalytically activematerials for facilitating the removal of unstable sulfur compounds fromthe crude oil by reaction of the unstable sulfur compounds to volatilesulfur species, including the conversion of unstable sulfur compounds toH₂S. Particulate catalytic material may fill at least a portion of thetreatment zone, or may be placed in trays within the treatment zone. Inembodiments, the heated crude oil passes through the particulatecatalyst trays, for conversion of the unstable sulfur compounds in thecrude oil.

In embodiments, the treatment zone comprises a reaction zone forconverting at least some of the unstable sulfur compounds in the crudeoil and for removing at least some of the volatile sulfur compounds fromthe crude oil. It will be appreciated that the process will beconsidered successful even though all of the unstable sulfur compoundsare not completely removed from the crude oil. The reaction zone may beintegral to or separate from the heating zone. The reaction zone mayinclude the capability for contacting the crude oil with a strippingfluid, the capability of contacting the crude oil with a catalyst orboth. Under at least some operating conditions, the sulfur-removalprocess is facilitated by integrating the reaction zone and theseparation zone into a single zone or vessel.

The reaction zone is generally a vessel in which a stripping fluidcontacts the crude oil for purposes of removing at least a portion ofthe volatile sulfur species from the crude oil. The reaction process maybe conducted in any vessel in which this contacting can occur, includinga storage tank, a holding tank in a transportation vessel, a pipethrough which the crude is passing, a distillation column, a reactionvessel, or a flash separator. The reaction vessel may comprise featuresto enhance the separation efficiency of the vessel.

Sweet stripping gas may be fed near the bottom of the treatment zone ata point below the crude oil feed and at a rate sufficient to provide apartial pressure of hydrogen sulfide to remove sufficient amounts of theunstable sulfur compounds to meet a specification based uponenvironmental specifications, shipping and transportation requirements,downstream operations such as refining or other uses. The stripping gasmay be fed at the bottom end of the zone or other location near thebottom end of the zone. The stripping gas bubbles up through the fallingcrude oil. While the gas moves upward through the zone it may becomeenriched with H₂S and other volatile sulfur containing materials andhydrocarbons. In embodiments, the treatment zone may comprise any vesselwhich facilitates the gas stripping, for example a spray tower, adistillation tower or a combination thereof. The crude oil may flowdownward through the tower internals such as, for example, structuredpacking, random packing, sieve trays, valve trays, and/or disk and donuttrays, or combinations thereof, becoming leaner in the content ofunstable sulfur compounds. Meanwhile, the stripping gas becomes richerin H₂S and other volatile sulfur compounds as it bubbles up the towerand exits the tower.

The rate at which the stripping fluid is added to the treatment zone isdetermined by a number of specific factors, including the viscosity andboiling range of the crude oil, the type of unstable sulfur compoundscontained therein, the quantity of contained unstable sulfur compounds,the nature and composition of the stripping fluid, the temperature andpressure of the treatment zone, and the like. Nevertheless, in anembodiment for an acceptable operating range for the stripping fluidrate, the stripping rate may be about 0.1 to about 1.0 MSCF per barrelof crude oil (about 18 to about 180 m³/m³) or about 0.25 to about 0.5MSCF per barrel of crude oil (44 to 89 m³/m³), or 0.3 to 0.4 MSCF perbarrel of crude (53 to 71 m³/m³).

A sulfur-containing stripping fluid is generated from the sulfur removalprocess. The sulfur-containing stripping fluid may also contain varyingamounts of light hydrocarbons from the crude oil, which are desirablyrecovered in a recovery unit such as a chilled vessel to condense thehydrocarbons, a mist screen to remove hydrocarbon mist droplets from thesulfur-containing stripping fluid or a knock-out pot to separate liquidsfrom the sulfur-containing stripping fluid. Recovering the hydrocarbonsfrom the sulfur-containing stripping fluid may be suitably handledeither within or outside and downstream of the treatment zone.

The treatment zone may further contain one or more catalytic materialsfor facilitating the conversion of unstable sulfur compounds to volatilesulfur species, including the conversion of unstable sulfur compounds toH₂S. Catalytic materials known to enhance the removal of the sulfurcompounds generally reduce the temperature at which the sulfur compoundsare usefully removed from the crude. Materials such as inorganic ororganic acids, particulate molecular sieves, dissolved metal ions,metal-containing slurry in an organic or aqueous fluid or a particulatecatalyst comprising a metal component on an inorganic oxide matrix aresuitable as catalytic materials for removing unstable sulfur compoundsfrom crude oil.

In embodiments, acids which are useful for the present process includeprotic acids, ionic materials with Lewis acid properties, and inorganicmaterials with acidic properties.

Among the protic acids, inorganic and organic acids may be used for thesulfur removal process. Inorganic acids, or catalytic materialscomprising inorganic acids, such as phosphoric acid and sulfuric acidare particularly beneficial. Hydrochloric acid will also remove sulfur,but a chlorine-containing acid is less desirable on account of possibledeleterious metallurgical effects. Catalytic materials containing Lewisacids are also useful for removing the sulfur compounds. Suitable Lewisacids including metals in ionic form such Fe³⁺, Zn²⁺, Co³⁺, Ni²⁺ may beused as a catalytic material. Molecular sieves, including mordenite andzeolite Y, either in hydrogen form and/or containing metal ions areuseful in the sulfur removal process. The metal ions may be incorporatedinto the molecular sieve during synthesis of the sieve, by ion exchangeor by impregnation of the molecular sieve. Methods for incorporatingmetallic species into the molecular sieve are well known. Amorphousinorganic oxide materials, such as silica, alumina, magnesia, titanic,and mixtures thereof, may also be used. Metals, such as Fe³⁺, Zn²⁺,Co³⁺, Ni²⁺, which are incorporated into the inorganic oxide material,either during preparation of the material or by impregnation, also showcatalytic activity for the conversion of unstable sulfur species. Thesecatalysts lower the operating temperature of pretreatment process, andat the same time keep good thermal and chemical stability during thecatalytic process.

The catalyst may be blended into the crude as a dissolved component oras a slurry. The dissolved component may be added to the crude as eitheran aqueous phase material or an organic phase material. Use of anaqueous phase material is generally monitored to prevent excess waterbeing added to the crude, since water in the presence of H₂S produces ahighly corrosive acid.

When added as a slurry, the catalytic material may be in the form of anorganometallic complex or an ionic species. Example catalysts added inthis way include the sulfates, nitrates, chlorides, acetates andsulfides of the metals in ionic form. The metals may further beassociated with finely divided support materials, such as alumina,silica or aluminosilicates.

In embodiments, the crude oil is contacted within the treatment zonewith at least one material known to have catalytic activity for theconversion of unstable sulfur compounds. The catalyst may be introducedinto the crude oil before the crude oil is introduced to the treatmentzone. In embodiments, the catalyst is added to the crude oil as adissolved material in a separate liquid phase, as a suspension in aseparate liquid phase or in powder or granular form added directly tothe crude oil. The separate liquid phase may be an aqueous fluid or anorganic fluid. In embodiments, the separate liquid phase liquid, whichcontains the catalyst material, is added to the crude in a ratio of upto 5 wt % of the crude oil. The separate liquid phase may comprise up to10 wt % catalytic material. Non-limiting examples include up to 10 wt %FeCl₃ dissolved in an aqueous fluid for addition to the crude.Non-soluble materials may be added to the crude as a slurry. The slurrymay have either an aqueous or an organic continuous phase.

In embodiments, the catalyst is present as a particulate catalyst. Theparticulate catalyst may be in the form of granules having uniform ornon-uniform shapes, including spheres, extrudates and other shapedmaterials, but other shapes are also within the scope of the particulatecatalyst. The granules are generally sized to have an averagecross-sectional dimension of greater than 100 μm. In embodiments, thegranules have an average cross-sectional dimension of greater than 1/32inch, or an average cross-sectional dimension of Greater than 1/16 inch.

When present in the treatment zone, the particulate catalyst may besituated such that the crude oil passing through the treatment zonepasses over the catalyst contained therein. The particulate catalyst maybe present in a fixed bed, a fluidized bed, a moving bed and the like.The particulate catalyst may be present in a single bed in the zone, orit may be present in multiple beds, each in a separate vessel, or inseparate layers in a single vessel, separated by, for example, a traywhich supports each bed. When a catalyst which is selected to remove theunstable sulfur from the crude is located in a fixed bed reactor, thecrude may pass downward through the catalyst bed, or it may flow upwardthrough the catalyst bed.

Each catalyst bed may comprise a single type of catalyst, or a mixtureof different catalysts. In a reaction zone containing multiple catalystbeds, the catalysts may vary from bed to bed in any order orconfiguration.

In embodiments, when at least one catalyst is present in the reactionzone, the reaction zone is maintained at a temperature in the region of100° F. to 450° F. The temperature may be selected to result in acertain level of sulfur removal from the catalyst. In embodiments, thecrude oil is maintained at a temperature in the range of 100° F. to 450°F. and at a pressure of 15 psia and above in the reaction zone. In somesuch embodiments, the crude oil is maintained at a temperature in therange of 100° F. to 450° F. and at a pressure in the range of 15 psia to200 psia for a time period in the range of 1 minute to 60 minutes. Anexemplary operating pressure is in the range of 15 psia to 100 psia.Exemplary residence time ranges include 5 to 40 minutes and 10 to 30minutes.

In embodiments, the crude oil with reduced unstable sulfur content (e.g.desulfurized crude oil) is passed from the treatment zone to adistillation column for separating the crude oil into its vapor phaseand liquid phase components. An exemplary distillation column includesan atmospheric column, an atmospheric crude column, a vacuum column or avacuum crude column. In embodiments, the treated crude oil istransported via ship, rail, barge, pipeline, truck or similar conveyanceprior to being passed to a distillation column. In embodiments, thecrude oil is heated in the treatment zone to crude distillationtemperatures, such as a temperature in the range of 600° F. to 800° F.The crude oil heated to this temperature is very reactive in thepresence of a catalyst, and the residence time within the treatment zoneis significantly reduced.

FIG. 1 illustrates an embodiment of the invention, including a crude oil5 passing through heating zone 10 for heating to reaction temperature.The heated crude oil 12 exiting the heating zone 10 at a temperature inthe range of 350° F. to 600° F. passes to the reaction zone 20, where atleast a portion of the unstable sulfur compounds are converted tovolatile sulfur compounds, including H₂S. The reaction zone 20 is atleast partially filled with packing material 25 which has little or nocatalytic activity for the conversion of the unstable sulfur compounds.The temperature in the reaction zone is sufficiently high to convert atleast a portion of the unstable sulfur compounds in the heated crude oil12. A stripping gas 14 is introduced to reaction zone 20, and at least aportion of a sulfur-containing stripping gas 16 is removed from thereaction zone. A crude oil with reduced sulfur content is recoveredthrough stream 18.

FIG. 2 illustrates another embodiment of the invention. In FIG. 2, thecatalytic material is containing within the reaction zone on catalystsupport trays. FIG. 2 illustrates a crude oil 105 passing throughheating zone 110 for heating to reaction temperature. The heated crudeoil 112 exiting the heating zone 110 at a temperature in the range of100° F. to 450° F. passes to the reaction zone 120 through crude oilinlet 122, where at least a portion of the unstable sulfur compounds areconverted to volatile sulfur compounds, including H₂S. The reaction zone120 contains catalyst support trays 125 on which a catalytic material isdistributed for contacting the crude oil passing therethrough. Astripping gas 114 is introduced to reaction zone 120 through fluid inlet124, and at least a portion of an sulfur-containing stripping gas 116 isremoved from the reaction zone. A crude oil with reduced sulfur contentis recovered through stream 118.

Example 1

Eocene crude is a Middle East crude having an API gravity of 18° and atotal sulfur content of 4.5 wt %.

The quantity of unstable sulfur compounds in a sample of Eocene crudeoil was determined as follows. 100 g Eocene crude oil sample was chargedto a flask equipped with an overhead condenser. A nitrogen stripping gasat a constant 50 cc/min was bubbled through the crude oil in the flask,which was quickly heated to and then maintained at 500° F. Gaseousreaction products from the crude oil (principally hydrogen sulfide andlight mercaptans) were passed through the overhead condenser to condensemost of the light hydrocarbons and return them to the flask. Thenitrogen gas containing the sulfur compounds was then passed through aNaOH scrubber to remove at least most of the sulfur compounds. Thenitrogen gas was then vented.

During the test, gas samples before the NaOH scrubber were sampled andtested in a Draeger's tube and confirmed in a gas chromatographic columnequipped with a sulfur chemiluminescence detector. It was found thatmost of the gaseous sulfur compounds were released from the crude oil inthe first 30 minutes; at times greater than 30 minutes, the amount ofsulfur released to the nitrogen gas decreased dramatically. After 3hours, the measured sulfur concentration in the nitrogen stream waslower than 1000 ppm.

To determine the amount of unstable sulfur, total sulfur contents in thecrude oil before and after the treatment were analyzed by the Lecosulfur method using a Leco SC-32 Sulfur Analyzer. Since only theunstable sulfur was released from the treatment, the total sulfurcontent difference between the original and the treated crude oil gavethe unstable sulfur content in this crude oil, which was calculated tobe about 0.5 wt % of the total crude oil. That accounts for ˜11% oftotal sulfur in the untreated crude oil.

Example 2

Example 1 was repeated with a typical heavy crude oil other than Eocenecrude, containing 3.8 wt % of total sulfur. No significant H₂S wasdetected in the N₂ effluent stream and the total unstable sulfur in thecrude was determined to be less than 0.005 wt % of the crude oil. Thus,it was determined that this heavy crude oil contained little or nounstable sulfur.

Example 3

Brönsted acids, including solid HY zeolite, acetic acid and phosphoricacid, were tested for their effectiveness as catalytic materials forremoving unstable sulfur compounds from crude oil. Each catalyticmaterial in turn was combined with 500 ml Eocene crude oil in a 1-literautoclave. The oil and catalyst mixture was heated under continuousstirring and a N2 stripping rate of 150 cc/min, at a constant operatingtemperature of 300° F. The operating pressure for the test was 100 psig,to keep light hydrocarbon in the oil in liquid form. The outlet gasstream was sampled and its H₂S concentration was measure using a GCequipped with a sulfur chemiluminescence detector.

At 300° F., both HY Zeolites and H₃PO showed a higher activity forproducing H₂S than did the control test without catalyst and also showeda higher activity for producing H₂S than did acetic acid. The data inTable 1 shows that the effectiveness of the catalytic material forremoving the unstable sulfur compounds depends on the concentration andthe acidity of the acid catalyst.

TABLE 1 Quantity of Peak H₂S concentration catalyst (T = 300° F.)Control: without catalyst 4,000 ppm Zeolite (HY):  4 wt % 55,000 ppmSi/Al weight ratio = 60 CH₃COOH 10 wt % 5,000 ppm H₃PO₄: 85%concentration 10 wt % 14,000 ppm

Example 4

Example 2 was repeated using powdered FeCl₃ as a typical Lewis acid saltat 200° F. Table 2 shows that FeCl₃ was particularly effective atremoving unstable sulfur compounds from crude oil.

TABLE 2 Quantity of Peak H₂S concentration catalyst (T = 200° F.)Control: without catalyst 75 ppm FeCl₃ 4 wt % 30,000 ppm

Example 5

Example 2 was repeated with a catalytic material comprising Fe (III) ionexchanged onto a Y zeolite. As shown in Table 3, the supported metal ionshowed considerable catalytic effects at 300° F.

TABLE 3 Quantity of Peak H₂S concentration catalyst (T = 300° F.)Control: without catalyst 4,000 ppm Zeolite (HY): 4 wt % 55,000 ppmSi/Al weight ratio = 60 Fe3+-Y zeolite 4 wt % 17,000 ppm

What is claimed is:
 1. A system for reducing a sulfur content of a crudeoil, including: a. a catalytic material comprising a metallic speciesselected from the group consisting of Fe³⁺, Zn²⁺, Co³⁺, and Ni²⁺; b. aheating zone configured for heating the crude oil in the absence ofadded hydrogen; c. a stripping fluid, configured for contacting theheated crude oil at a temperature in a temperature range of 100° F. to450° F., a pressure in a pressure range of 15 psia to 200 psia, and inthe presence of the catalytic material; and d. a treatment zonecomprising a fluid inlet configured for passing the stripping fluid intothe treatment zone, a crude oil inlet configured for passing the heatedcrude oil into the treatment zone, and a bed of the catalytic materialpositioned within the treatment zone such that the heated crude oil andthe stripping fluid are together contacted within the bed of thecatalytic material; wherein the stripping fluid comprises a gas-phasematerial selected from the group consisting of the natural gas, amethane, an ethane, a propane, a butane, a pentane and heavierhydrocarbons, a nitrogen, a carbon dioxide, an argon, a helium, a carbonmonoxide and combinations thereof.
 2. The system of claim 1, wherein theheating zone comprises a temperature in the temperature range of 100° F.to 450° F. and a pressure in the pressure range of 15 psia to 200 psia.3. The system of claim 2, wherein the crude oil is in the heating zonefor a time period in a time range of 1 minute to 60 minutes.
 4. Thesystem of claim 2, wherein the crude oil contains at least 0.1 wt %unstable sulfur compounds prior to heating, and wherein at least 50% ofthe unstable sulfur compounds are converted into volatile sulfurcompounds upon heating.
 5. The system of claim 4, wherein the unstablesulfur compounds comprise polysulfanes and polysulfides.
 6. The systemof claim 4, wherein the unstable sulfur compounds comprise a sulfurcompound having a generic formula Sx, wherein x is a value from 1 to 10.7. The system of claim 4, wherein the volatile sulfur compounds compriseH2S, low molecular weight mercaptans, carbon disulfide, carbonylsulfide, and mixtures thereof.
 8. The system of claim 4, wherein thevolatile sulfur compounds are removed in the treatment zone.
 9. Thesystem of claim 8, wherein the crude oil is reduced in the sulfurcontent in the absence of added caustic alkali compounds, aminecompounds, oxidation agents and organic reducing agents.
 10. The systemof claim 1, wherein a desulfurized crude oil and a sulfur containingstripping gas are recovered from the treatment zone.
 11. The system ofclaim 1, further comprising an atmospheric distillation column, whereina desulfurized crude oil is passed through the distillation column. 12.The system of claim 1, further comprising contacting the crude oil withat least one aqueous solution containing at least one sulfur-containingcompound selected from the group consisting of ammonium sulfide andsodium thiosulfate and recovering a solution containing an increasedamount of sulfur.
 13. The system of claim 1, wherein the catalyticmaterial is selected from the group consisting of inorganic acids ororganic acids, particulate molecular sieves, dissolved metal ions,metal-containing slurry in an organic or aqueous fluid and a particulatecatalyst comprising a metal component on an inorganic oxide matrix. 14.The system of claim 1, wherein the catalytic material comprises aninorganic oxide selected from the group consisting of Y zeolites,silica, alumina, silica alumina and mixtures thereof.
 15. The system ofclaim 1, wherein the catalytic material comprises an inorganic acidselected from the group consisting of phosphoric acid and sulfuric acid.16. The system of claim 1, wherein the catalytic material is maintainedas a fixed particulate bed.
 17. The system of claim 1, wherein thestripping fluid comprises the gas-phase material selected from the groupconsisting of the natural gas, the nitrogen, and the combinationsthereof.
 18. The system of claim 1, wherein the stripping fluidcomprises the nitrogen.